1. Field of the Invention
The present invention relates to an image forming unit, a latent image carrier unit, a developing unit and an image forming apparatus. In particular, the present invention relates to an image forming unit, a latent image carrier unit, a developing unit and an image forming apparatus which are characterized by a mechanism for enabling the user to replace the latent image carrier unit (or photosensitive drum unit) and the developing unit independently of each other and a mechanism for pressing a developing roller of the developing unit onto a photosensitive drum of the photosensitive drum unit, operable following at least one of a mounting movement when the photosensitive drum unit is mounted to the developing unit and a driving movement in the image forming unit.
2. Description of the Related Art
The image forming apparatus of an electronic photographic recording system, such as a copier or a printer, has widely prevailed in office use due to its high operation speed, high resolution and low noise, and the market thereof has recently been widened even to a personal use in which a lower machine cost, a smaller machine size and/or a higher resolution image are required.
In the prior art printer of an electronic photographic recording system using a static latent and image forming process, a static latent image is formed on a uniformly charged surface of a photosensitive drum by exposing it to a laser optical system or an LED array system in accordance with image information.
Then, in a developing process, a visible toner image is developed by sticking charged toner onto the static latent image on the photosensitive drum by using a developing roller, and the toner image is then statically transferred to a recording medium by using a transfer device. Thereafter, the transferred visible image is fixed on the recording medium by heat, pressure or light, and the recording medium is discharged to a stacker.
In such a printer of an electronic photographic recording system, the toner not transferred but left on the surface of the photosensitive drum is removed therefrom by a cleaning blade, and returned to a toner box of the developing unit through a toner returning mechanism for repeated use. The printer of an electronic photographic recording system provided with such a toner returning mechanism will be described below with reference to FIGS. 20 and 21.
In FIG. 20, a structure of one example of the printer of an electronic photographic recording system with the prior art toner returning mechanism is conceptually illustrated, wherein a photosensitive drum unit 60 includes a photosensitive drum 61 and a cleaning unit 62 having a cleaning blade 63 arranged with the drum in a unit, and a developing unit 70 is detachably mounted to the photosensitive drum unit 60 to form an image forming unit which in turn is detachably mounted to a printer device 100.
The developing unit 70 is provided with a doctor blade 71, a developing roller 72 comprising a magnetic roller and a sleeve, agitators 73 and 74 and a toner chamber 75. A toner cartridge 83 is detachably mounted to the developing unit 70, for dispensing toner into the developing unit 70 through an opening provided in a cartridge support member 81.
In the image forming unit of such a structure, a toner returning mechanism 90 is provided to couple the cleaning unit 62 of the photosensitive drum unit 60 to the toner chamber 75 of the developing unit 70 for recycling the toner which is not transferred but is removed from the photosensitive drum 61 by the cleaning unit 62.
A corona charger 86 is arranged at the opening in the housing of the image forming unit, and a transfer device 87 is disposed beneath the photosensitive drum unit 60. An optical unit 88 such as an LED array is disposed downstream from the corona charger 86 in the sense of the rotational direction of the photosensitive drum.
In the above-mentioned printer of an electronic photographic recording system, after the photosensitive drum 61 is uniformly charged by the corona charger 86, a static latent image is formed on the surface thereof by a light from the optical unit 88 in accordance with image information or printing information, and conveyed to a developing zone as the photosensitive drum 61 rotates. In the developing zone, a toner layer on the developing roller 72 is attracted to the static latent image on the photosensitive drum 61 by static attraction to form a visible toner image which in turn is transferred to the recording medium by the transfer device 87 and then fixed by the fixing device 88. Finally, the recording medium 110 on which the visible image has been fixed is discharged to a stacker 101.
In this connection, the surface of the photosensitive drum 61 is cleaned by the cleaning blade 63 after the transfer, and the removed toner is received by a waste toner tank 64 of the cleaner unit 62. Thereafter, the surface of the photosensitive drum 61 is decharged by a decharging means (not shown) to resume the initial state.
The non-transferred waste toner is made to return from the cleaner unit 62 to the toner chamber 75 of the developing unit 70 through the toner returning mechanism 90.
FIG. 21 is a plan view of the above-mentioned toner returning mechanism 90 including a flexible tube 91 and a rotatable coil member 92 accommodated in the flexible tube 91. One end of the coil member 92 is connected to a helical gear 94 intermeshed with a helical gear 93 rotating in association with a coil member 76 provided in the waste toner tank 64 to return the waste toner in the waste toner tank 64 to the toner chamber 75 via the flexible tube 91.
In the printer of an electronic photographic recording system with the prior art toner returning mechanism 90, it is substantially impossible for the user to replace the photosensitive drum unit 60 and the developing unit 70 separately from each other although the developing unit is apparently detachable from the photosensitive drum unit 60, since the toner returning mechanism 90 is firmly connected to the photosensitive drum unit 60 and the developing unit 70.
In an example of a specification, for example, the developing unit is guaranteed to perform the printing of approximately ten thousand sheets, while the photosensitive drum unit is guaranteed to perform the printing of approximately fifty thousand sheets. In the printer of an electronic photographic recording system with the prior art toner returning mechanism, however, the image forming unit consisting of the photosensitive drum unit and the developing unit as described above must be replaced as a one-piece part, which means that the duration of replacement life of the image forming unit is necessarily matched with the developing unit having a shorter duration of replacement life, whereby it is impossible to effectively use the photosensitive drum.
In this regard, the duration of life of the developing unit is decided by that of the developing roller and/or an amount of toner contained therein, while the duration of life of the photosensitive drum unit is decided by that of the photosensitive drum.
A single component developing method using a non-magnetic developing agent, particularly in such a method of a contact developing system wherein the development is carried out by the contact of the photosensitive drum with the developing roller is believed advantageous for realizing the above-mentioned requirement for low cost, size reduction or high resolution image quality. However, printing defects, such as blur, are liable to occur in the above method if the photosensitive drum and the developing unit are detachably connected to each other so that the user is capable of replacing one of them with a fresh one, unless the photosensitive drum is assuredly in tight contact with the developing roller.
To solve such a problem, an object of the present invention is to provide an image forming unit in which a photosensitive drum unit and a developing unit are replaceable independently of each other by a user.
Also, another object of the present invention is to enable a user to independently replace the photosensitive drum unit or the developing unit from each other, and to assuredly bring them into tight contact with each other.
According to the present invention, an image forming unit comprises a latent image carrier unit and a developing unit detachably mounted to each other, characterized by an engagement mechanism for detachably engaging a waste toner receptacle provided in the latent image carrier unit with a toner returning mechanism provided in the developing unit, and an opening/closing mechanism for delivering the toner from the waste toner receptacle to the toner returning mechanism.
In this structure, it is possible for the user to replace the latent image carrier unit and the developing unit independently of each other so that the respective unit is effectively usable until the duration of the life thereof has lapsed. For example, a shutter may be provided as part of the opening/closing mechanism for delivering the toner into the toner returning mechanism.
Also, according to the present invention, an image forming unit is characterized by a pressing device operable following at least one of a mounting movement when the latent image carrier unit is mounted to the developing unit and a driving movement in the image forming unit for pressing a developing roller of the developing unit onto a latent image carrier of the latent image carrier unit.
In this structure, it is possible to assuredly bring the developing roller into tight contact with the latent image carrier irrespective of the positional accuracy of an image forming unit supporting mechanism provided in a main body of an image forming apparatus, whereby the generation of printing defects is avoidable.
Preferably, the pressing device comprises a lever opening/closing mechanism provided in the latent image carrier unit. By providing the lever opening/closing mechanism in the latent image carrier unit and engaging the same with an engagement means provided in the developing unit as described above, it is possible to easily press the developing roller onto the latent image carrier. Or, the pressing device comprises a lever opening/closing mechanism provided in the latent image carrier unit and a mechanism for rotating the developing roller by a drive force derived from the main body of the image forming apparatus. By providing the mechanism for rotating the developing roller driven by driving force derived from the main body of the image forming apparatus, together with the lever opening/closing mechanism as described above, to displace the developing roller toward the latent image carrier about a rotating shaft, it is possible to more assuredly press the developing roller onto the latent image carrier. Or, the pressing device comprises a lever opening/closing mechanism provided in the latent image carrier unit, a mechanism for rotating the developing unit driven by a drive force derived from the main body of the image forming apparatus, and a mechanism for rotating the image carrier driven by a drive force derived from the main body of the image forming apparatus. By providing the mechanism for rotating the image carrier driven by a drive force derived from the main body of the image forming apparatus, together with the lever opening/closing mechanism and the developing unit rotating mechanism, and by changing a torque thereof into a pressing force as described above, it is possible to more assuredly press the developing roller onto the latent image carrier in a follow-up manner.
Preferably, a projection is provided in the latent image carrier unit to be in contact with a projection provided in the developing unit when the latent image carrier rotates so that a force is generated due to a torque from the latent image carrier rotating mechanism, for pressing the developing unit onto the latent image carrier in a follow-up manner. As a mechanism for changing the torque of the latent image carrier to the pressing force, projections are preferably provided both in the latent image carrier unit and the developing unit, whereby a force pressing the developing unit onto the latent image carrier in a follow-up manner is assuredly generated even by such a simple structure.
Favorably, the lever opening/closing mechanism includes an engagement lever to be engaged with a slidable lever provided in the developing unit and connected to a spring member. By using the slidable lever connected to the spring member in the developing unit as a structure to be engaged with the engagement lever constituting the lever open/close mechanism, a stable pressing force is obtainable by the action of the spring member.
Preferably, a projection is provided in the latent image carrier unit to be engaged with a groove provided in a side wall of the developing unit so that a force pressing the developing unit onto the latent image carrier in a follow-up manner is obtained due to the torque accompanied with the opening/closing operation of the lever opening/closing mechanism. By providing the projection in the latent image carrier unit to be engaged with the groove provided in the side wall of the developing unit as described above, it is possible to generate a further follow-up pressing force due to the torque accompanied with the opening/closing operation of the lever-opening/closing mechanism, to result in a more reliable press-contact.
Preferably, the lever opening/closing mechanism provided in the latent image carrier unit is also used as an opening/closing mechanism for delivering the toner from the bottom of the waste toner receptacle into the toner returning mechanism provided in the developing unit. Thereby, an effective separation mechanism for the image forming unit having the toner returning mechanism is obtainable, which simplifies an overall structure.
Also, according to the present invention, a latent image carrier unit is provided, which is characterized in that a drive means for driving an opening/closing mechanism is provided for delivering the toner into the toner returning mechanism provided in the developing unit. By providing the driving mechanism for driving the opening/closing mechanism for delivering the toner into the toner returning mechanism provided in the developing unit, for example, a pressing member for rotating a shutter in association with the lever opening/closing mechanism, a latent image carrier unit is obtainable which is capable of being replaced as an independent part independently from the developing unit.
Also, according to the present invention, a latent image carrier unit is provided which is characterized in that a pressing device is provided for pressing the developing roller of the developing unit onto the latent image carrier of the latent image carrier unit. The pressing device is operable following at least one of a mounting movement when the latent image carrier unit is mounted to the developing unit and a driving movement in the image forming unit. By providing the pressing device, it is possible to simplify the pressing mechanism in the image forming unit of a contact development system.
Also, according to the present invention, the pressing device is constituted by a lever opening/closing mechanism including an engagement lever engaged with a slide lever connected to a spring member provided in the developing unit.
Also, according to the present invention, a developing unit is provided which is characterized in that, in the toner returning mechanism, an engagement mechanism is provided to be releasably engaged with the bottom of the waste toner receptacle provided in the latent image carrier unit, and an opening/closing mechanism is provided for delivering the toner into the toner returning mechanism from the bottom of the waste toner receptacle. By providing the engagement mechanism to be releasably engaged with the bottom of the waste toner receptacle provided in the latent image carrier unit and the opening/closing mechanism for delivering the toner into the toner returning mechanism from the bottom of the waste toner receptacle, it is possible to constitute the developing unit as an independent part to be replaced independently from the latent image carrier unit. In this regard, part of the opening/closing mechanism may be constituted by a shutter.
Also, according to the present invention, a developing unit is provided which is characterized in that a pressing device is provided in a manner similar to the above.
Also, according to the present invention, an image forming apparatus is provided which comprises an image forming unit wherein a latent image carrier unit and a developing unit are detachably mounted to each other is provided, characterized in that an engagement mechanism is provided for releasably engaging a waste toner receptacle provided in the latent image carrier unit with a toner returning mechanism provided in the developing unit, and an opening/closing mechanism is provided for delivering the toner from the bottom of the waste toner receptacle into the toner returning mechanism. By this structure, it is possible to constitute an image forming apparatus from which the developing unit and the latent image carrier unit are replaceable independently from each other. Part of the opening/closing mechanism for delivering the toner into the toner returning mechanism may be constituted by a shuffer.
Also, according to the present invention, an image forming apparatus is provided which comprises an image forming unit wherein a latent image carrier unit and a developing unit are detachably mounted to each other, characterized by means for pressing a developing roller constituting the developing unit onto a latent image carrier constituting the latent image carrier unit in a follow-up manner in association with at least one of the operation for mounting the latent image carrier unit to the developing unit and the operation for driving the image forming unit. In this structure, it is possible to constitute an image forming apparatus of a contact development system capable of assuredly pressing the latent image carrier onto the developing roller.